The present study was aimed to ascertain the levels of seven polychlorinated biphenyls (PCBs) in patients with cancers of the digestive system in comparison to normal healthy subjects. Fasting blood samples were collected from the donors with informed consent and the isolated sera of each sample was extracted with organic solvents and analyzed for the residues of PCBs with Gas Chromatograph coupled with Electron Capture Detector (GC-ECD). Mean level of total PCBs (ΣPCBs) was found significantly elevated in the cancer patients (2.555 mg/kg) compared with the healthy subjects (0.361 mg/kg). PCB 52 was detected in high concentrations compared with other PCB congeners with a level of 1.629 mg/kg in the cancer patients and 0.12 mg/kg in the healthy subjects. All of the cancer samples (100 %) and 91.42 % of the healthy subjects were detected positive for the presence of PCBs. Highest mean level of ΣPCBs (7.259 mg/kg) was found in cancer cases of the gall bladder while lowest mean level (0.44 mg/kg) was found in cases of the small intestine. Concentrations and frequencies of the studied individual PCB congeners (PCB-28, PCB-52, PCB-101, PCB-138, PCB-153, PCB-180 and PCB-209) as well as ΣPCBs were found significantly elevated in the cancer cases compared with the healthy subjects. It can be concluded from the obtained results that PCBs have a positive association with the risk of cancer of the digestive system. These persistent chemicals which circulate in various environmental compartments including humans seem to have a role in the chemical basis of carcinogenesis.